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There’s more to seminal fluid, which makes up to 70% of semen’s composition, than procreation. Scientists are only recently beginning to understand how the seminal fluid is interacting with the female brain and body, and findings so far may be surprising for some. For instance, in animals – including humans – semen affects the female reproductive tract, to maximize the chances of conception. But it doesn’t stop here. The influence of semen on females might go even beyond this. In experiments on fruit flies, scientists found the females had altered gene expression post semen exposure, while males produce more seminal proteins when there are more rivals. Suddenly, semen just got a heck of a lot more complicated.

When you think about it, though, it makes sense for semen to be complicated, considering its role in reproduction. After all, physiological responses are often interconnected. It’s all about maximising the chances of the male reproducing,” says Sarah Robertson of the University of Adelaide in Australia.

The most important finding reported at the Society for Molecular Biology and Evolution conference in Vienna was that one of the seminal proteins was a sort of “master regulator” of genes, as the female fruit flies showed a wide range of changes in gene expression.

The seminal fluid can also make the females eat more, lay more eggs and be less receptive to other males. The real question, though, is whether the same applies to humans as well. It might very well happen, considering semen protein signaling is so wide-spread in the animal kingdom.

Some claim semen makes women sleepy. But the most interesting finding might be that semen exposure helps curb depression. A study from 2002 found after surveying 300 students that women whose partners did not use condoms scored lower on a measure of depression. If this is genuinely true, then the next anti-depressants might be based on semen. Imagine that.

But how does that happen? How would semen alter brain chemistry? Well, in fruit flies at least, semen proteins enter the circulatory system and end up in the brain. In humans, this is less likely. Instead, the signaling molecules might elicit a response in the uterus which in turns causes a physical response that’s later transferred to the brain. Whatever’s the case, it’s amazing to hear that something so often disregarded as semen can have widespread physiological responses.